Introduction: Environmental temperature has a significant effect on human physiological response to physical activity. Therefore, the purpose of this study was to explore the changes in levels of cortisol and lactate of athletes’ blood after one exercise session in cold, warm and natural environments. Materials and Methods: Ten young male athletes (22±2 years 67.4±2.7 kg) ran on a treadmill for 1h with 60% VO2max in conditions of natural (22±1˚c, 50±5 RH), cold (3±1˚c, 50±2 RH) and warm (35±1˚c, 50±5RH) environments. Blood samples were collected to measure lactate and cortisol, before, after exercise and at 2h recovery. In addition, body temperature, pressure scale and water consumed by athletes water during exercise were measured. In order to analyze data, Repeated Measure and Bonferroni tests at the significant level of p<0.05 were utilized. Results: Amounts of cortisol and lactate increased significantly after exercise, in all these conditions (p<0.0001). Lactate levels increased significantly after exercise in a warm environment, compared to cold and natural environments (p<0.0001). In addition, cortisol increased significantly in a warm environment in comparison to cold (p=0.037) and natural (p=0.016) environments. Significant differences were observed in cortisol and lactate levels after a rest between excercise in warm and natural environments (p=0.036, p=0.007). Conclusion: Exercise causes accumulation of lactate and release of cortisol in the three environments. It seems that exercise in a warm environment, in comparison with colder environments, causes greater increases in body and muscle temperature, physical pressure, cardiovascular changes, and hence prevents their to returning initial levels during the recovery period.